The early Muslim conquests began with the Islamic prophet Muhammad in the 7th century. He established a new unified polity in the Arabian Peninsula which under the subsequent Rashidun and Umayyad Caliphates saw a century of rapid expansion.

The resulting empire stretched from the borders of China and the Indian subcontinent, across Central Asia, the Middle East, North Africa, and parts of Europe (Sicily and the Iberian Peninsula to the Pyrenees). Edward Gibbon writes in The History of the Decline and Fall of the Roman Empire:

“Under the last of the Umayyads, the Arabian empire extended two hundred days journey from east to west, from the confines of Tartary and India to the shores of the Atlantic Ocean ... We should vainly seek the indissoluble union and easy obedience that pervaded the government of Augustus and the Antonines; but the progress of Islam diffused over this ample space a general resemblance of manners and opinions. The language and laws of the Quran were studied with equal devotion at Samarcand and Seville: the Moor and the Indian embraced as countrymen and brothers in the pilgrimage of Mecca; and the Arabian language was adopted as the popular idiom in all the provinces to the westward of the Tigris.”

The Muslim conquests brought about the collapse of the Sassanid Empire and a great territorial loss for the Byzantine Empire. The reasons for the Muslim success are hard to reconstruct in hindsight, primarily because only fragmentary sources from the period have survived. Fred McGraw Donner suggests that formation of a state in the Arabian peninsula and ideological (i.e., religious) coherence and mobilization was a primary reason why the Muslim armies in the space of a hundred years were able to establish the largest pre-modern empire until that time. The estimates for the size of the Islamic Caliphate suggest it was more than thirteen million square kilometers (five million square miles). Most historians agree as well that the Sassanid Persian and Byzantine Roman empires were militarily and economically exhausted from decades of fighting one another.

It has been suggested that some Jews and Christians in the Sassanid Empire and Jews and Monophysites in Syria were dissatisfied and welcomed the Muslim forces, largely because of religious conflict in both empires. It has also been suggested that later Syriac Christians reinterpreted the events of the conquest to serve a political or religious interest. At other times, such as in the Battle of Firaz, Arab Christians allied themselves with the Persians and Byzantines against the invaders. In the case of Byzantine Egypt, Palestine and Syria, these lands had been reclaimed from the Persians only a few years before.

The death of Muhammad confronted the infant Muslim community with something in the nature of a constitutional crisis. The Prophet had left no provision for the succession, nor had he even created a council on the lines of the tribal Majlis which might have exercised authority during the crucial transition period. The unique and exclusive character of the authority which he claimed as sole exponent of God's will would not have allowed him to nominate a colleague or even a successor-designate during his lifetime. The later tradition of the nomination by the Prophet of his cousin 'All, who married his daughter Fatima, is accepted only by the Shia.

The concept of legitimate succession was foreign to the Arabs at the time, and it is probable that even if Muhammad had left a son the sequence of events would not have been different. The fate of Moses supports this view. The Arab tradition that the Sheikh should be chosen from a single family seems to have had little effect, and in any case the claims of fathers-in-law like Abu Bakr, or sons-in-law like 'All, can have had little force as such in a polygamous society. The Arabs had only one precedent to guide them — the election of a new tribal chief. The Medinese proceeded to choose one from among the tribe of Khazraj, thus incidentally revealing the limitations of their conversion.

The Ridda Wars (Arabic: حروب الردة‎), also known as the Wars of Apostasy, were a series of military campaigns launched by the Caliph Abu Bakr against rebel Arabian tribes during 632 and 633, just after Muhammad died. The rebels' position was that they had submitted to Muhammad as the prophet of God, but owed nothing to Abu Bakr. Some rebels followed either Tulayha or Musaylima or Sajjah, all of whom claimed prophethood. Most of the tribes were defeated and reintegrated into the Caliphate. The peoples surrounding Mecca did not revolt.

Geophysical map of the Caucasus area with major settlements and regions, overlaid with green for Umayyad territory, yellow for Khazar territory, and red for Byzantine territory.

The Arab–Khazar wars were a series of conflicts fought between the armies of the Khazar Khaganate and the Rashidun, Umayyad, and Abbasid caliphates and their respective vassals.

Historians usually distinguish two major periods of conflict, the First Arab–Khazar War (c. 642-652) and Second Arab-Khazar War (c. 722-737), but the Arab-Khazar military confrontation also involved sporadic raids and isolated clashes from the middle of the 7th century to the end of the 8th century.

The Arab-Khazar wars were a result of the attempts of the Umayyad Caliphate to secure control of Transcaucasia and the North Caucasus, where the Khazars were already established. The first Arab invasion, in the 640s and early 650s, ended with the defeat of an Arab force led by Abd ar-Rahman ibn Rabiah outside the Khazar town of Balanjar. Hostilities broke out again with the Caliphate in the 710s, with raids back and forth across the Caucasus Mountains. Led by the distinguished generals al-Jarrah ibn Abdallah and Maslama ibn Abd al-Malik, the Arabs were able to capture Derbent and even the southern Khazar capital of Balanjar, but these successes had little impact on the nomadic Khazars, who continued to launch devastating raids deep into Transcaucasia. In one such raid in 730, the Khazars inflicted a major defeat on the Umayyad forces at the Battle of Ardabil, killing al-Jarrah, but were in turn defeated the next year and pushed back north. Maslama then recovered Derbent, which became a major Arab military outpost and colony, before being replaced by Marwan ibn Muhammad (the future caliph Marwan II) in 732. A period of relatively localized warfare followed until 737, when Marwan led north a massive expedition that reached the Khazar capital Atil on the Volga. After securing some form of submission by the khagan, the Arabs withdrew.

The 737 campaign marked the end of large-scale warfare between the two powers, establishing Derbent as the northernmost Muslim outpost and securing Muslim dominance over Transcaucasia. At the same time, the continuing warfare weakened the Umayyad army and contributed to the eventual fall of the dynasty to the Abbasid Revolution a few years later. Relations between the Muslims of the Caucasus and the Khazars remained largely peaceful thereafter, apart from two Khazar raids in the 760s and in 799, resulting from failed efforts to secure an alliance through marriage between the Arab governors or local princes of the Caucasus and the Khazar khagan. Occasional warfare continued in the region between the Khazars and the Muslim principalities of the Caucasus until the collapse of the Khazar state in the late 10th century, but the great wars of the 8th century were never repeated.

The Arab-Byzantine wars were a series of wars between the mostly Arab Muslims and the Byzantine Empire between the 7th and 11th centuries AD, started during the initial Muslim conquests under the expansionist Rashidun and Umayyad caliphs in the 7th century and continued by their successors until the mid-11th century.

The emergence of Muslim Arabs from Arabia in the 630s resulted in the rapid loss of Byzantium's southern provinces (Syria and Egypt) to the Arab Caliphate. Over the next fifty years, under the Umayyad caliphs, the Arabs would launch repeated raids into still-Byzantine Asia Minor, twice threaten the Byzantine capital, Constantinople, with conquest, and outright conquer the Byzantine Exarchate of Africa. The situation did not stabilize until after the failure of the Second Arab Siege of Constantinople in 718, when the Taurus Mountains on the eastern rim of Asia Minor became established as the mutual, heavily fortified and largely depopulated frontier. Under the Abbasid Empire, relations became more normal, with embassies exchanged and even periods of truce, but conflict remained the norm, with almost annual raids and counter-raids, sponsored either by the Abbasid government or by local rulers, well into the 10th century.

During the first centuries, the Byzantines were usually on the defensive, and avoided open field battles, preferring to retreat to their fortified strongholds. Only after 740 did they begin to launch counterstrikes of their own, but still the Abbasid Empire was able to retaliate with often massive and destructive invasions of Asia Minor. With the decline and fragmentation of the Abbasid state after 861 and the concurrent strengthening of the Byzantine Empire under the Macedonian dynasty, the tide gradually turned. Over a period of fifty years from ca. 920 to 976, the Byzantines finally broke through the Muslim defences and restored their control over northern Syria and Greater Armenia. The last century of the Arab–Byzantine wars was dominated by frontier conflicts with the Fatimids in Syria, but the border remained stable until the appearance of a new people, the Seljuk Turks, after 1060.

The Arabs also took to the sea, and from the 650s on, the entire Mediterranean Sea became a battleground, with raids and counter-raids being launched against islands and the coastal settlements. Arab raids reached a peak in the 9th and early 10th centuries, after the conquests of Crete, Malta and Sicily, with their fleets reaching the coasts of France and Dalmatia and even the suburbs of Constantinople.